upgrading just one "stable" package to "testing" version

[Toby Thain <toby@telegraphics.com.au>]

Hi,

I've just upgraded one Debian 2.2 machine from stable to testing and 
other 2.2 stable machines can't ssh into it ("Disconnecting: Bad 
packet length 1349676916"). So I'd like to upgrade ssh on the client 
machine to the "testing" version. But I don't know how to do this 
other than adding "testing" to the apt-get sources, dselect upgrade, 
etc., which will upgrade everything. Can anyone explain to me how to 
be more selective?

Thanks
Toby